The present invention relates to a tip turbine engine, and more particularly to an integral engine case surrounding the engine fan, combustor, and turbine.
An aircraft gas turbine engine of the conventional turbofan type generally includes a forward bypass fan and a low pressure compressor, a middle core engine including a combustor, and an aft low pressure turbine all located along a common longitudinal axis. Although highly efficient, conventional turbofan engines operate in a axial flow relationship. The axial flow relationship results in a relatively complicated elongated engine structure and therefore requires separate engine cases for the bypass fan, low pressure compressor, combustor, and low pressure turbine. Each engine case may further include several joints and structural attachments, often making assembly of the engine cases laborious and expensive.
A recent development in gas turbine engines is the more longitudinally compact tip turbine engine. Tip turbine engines locate an axial compressor forward of a bypass fan, which includes hollow fan blades that receive airflow from the axial compressor therethrough such that the hollow fan blades operate as a centrifugal compressor. Compressed core airflow from the hollow fan blades is mixed with fuel in an annular combustor located radially outward from the fan. The combustor ignites the fuel mixture to form a high energy gas stream which drives turbine blades that are integrated onto the tips of the hollow bypass fan blades for rotation therewith as disclosed in U.S. Patent Application Publication Nos.: 2003192303; 20030192304; and 20040025490. The tip turbine engine provides a thrust to weight ratio comparable to conventional turbofan engines of the same class within a package of significantly shorter longitudinal length.
Accordingly and because of the shorter longitudinal length of the tip turbine engine, it is desirable to eliminate the laborious and expensive assembly of several cases by providing an integrated one-piece engine case for the engine fan, combustor, and turbine.